Continuous process of converting vegetable stock to paper pulp



Dec. 12, 1961 R. w. POLLEYS 3,012,927

CONTINUOUS PROCESS OF CONVERTING VEGETABLE STOCK TO PAPER PULP Filed Sept. 11, 1957 FROM RECORDING a Fig. l

TOTALIZING FLOW METER TEMP. CONTROL CHEMICAL IITIIIIIII 22 I I I I STEAM J I T I r I I I I 2| I l I I I I 24 CHEMICAL I H I H4 1 52%: FRESH WATER I E SUPPLY I HEATER WEIGHING f V 23 CONVEYOR I l l I I I I I i /TEMP. CONTROL I I I .5 I Q I I I sTEAM E i wHITE I I I I l5 LIQUOR I I I6 CAUSTIC T '4 I FQD J HEATER '9 MIXING l9 l8 l7 WHITE CONVEYOR LIQUOR LEVEL LEVEL 27/3} INDICATOR INDICATOR 28 .DIGESTER REJECTS TOTALIZING M ETE R INVENTOR.

BLOVII TANK 2 FROM RECORDING if CAUSTIC STORAGE United States Patent 3,012,927 CONTINUOUS PROCESS OF CONVERTING VEGE- TABLE STOCK TO PAPER PULP Richard W. Polleys, North Andover, Mass, assignor to Process Evaluation and Development Corporation,

New York, N.Y., a corporation of Delaware Filed Sept. 11, 1957, Ser. No. 683,246 5 Claims. (Cl. 162--17) This invention comprises a new and improved process for insuring the supply and accurate proportioning of digestant liquors, moisture, and raw vegetable fiber in a continuous conversion of such raw material as bagasse or wood into paper pulp. The invention includes Within its scope the novel apparatus herein shown as employed in earring out the said process.

Much effort has been expended in the design and operation of process and apparatus for the continuous production of paper pulp, but heretofore their success has depended largely upon the detailed supervision and skilled regulation of the supply of the three principal components which are eventually delivered to the digester. Any serious deviation from the optimum conditions immediately results in impaired product and loss to the manufacturer.

I have discovered that the cost of supervision may be substantially reduced and the uniformity of the ultimate product assured by the process of my invention which is characterized by continuously sending information signals mechanically indicating or recording at a central station the rate of delivery of the raw stock and the digestant liquor, and automatically controlling from said central station the rate of feed of each component by transmitting control impulses in accordance with the information signals so received. Preferably and as herein shown the rate of flow of water to the system may also be indicated by information signals received continuous ly and recorded at the same central station and its rate of flow automatically controlled by impulses transmitted continuously therefrom. Accordingly, after making suitable preliminary manual adjustment for the work in hand, the process may be turned over to automatic control with very great advantage in all the respects above discussed. In preparing bagasse for the manufacture of paper pulp, and in many other instances where it is desired to separate relatively short and broad or heavy fines from long and narrow or light fibers or fiber bundles, vibrating conveyors as heretofore known have not been entirely satisfactory because certain of the longer or heavier components are likely to dive through fine mesh screens along with the shorter or broader fines. For instance, if a mass of sugar cane bagasse is passed over a grasshopper conveyor screen of /8" round or square mesh, the resulting fines may contain not only pith and sand but up to as much as 20% of fiber bundles less than /8" in diameter but of very substantial length, sometimes up to as much as 2". The fiber thus lost is useful for pulp making, and if the pith is to be used as a basis for certain valuable by-products, it must be as nearly as possible free from fiber bundles which, if mixed with molasses for cattle feed, would cause intestinal irritation.

The characteristics of the process and the character of the apparatus employed will be best understood and ap- 'ice preciated from the following description of the preferred manner of carrying out the process as shown in the accompanying drawing in which the drawing is a diagrammatic flow sheet.

In this diagram solid lines indicate the path of movement of the raw material from the time it leaves the screening conveyors until it is discharged from the digester to the blow tank. The path of travel of the digestant liquor, water and steam is also indicated in full lines, whereas the path of the information signals to the control station is indicated in dash lines and of the control impulses from the control station to the various valves and gate is indicated in dotted lines.

The raw paper making fiber having been first selectively screened is conveyed from the screening station through an automatically operated control gate 10 to the weighing conveyor which is equipped with recording and controlling devices operating to vary the speed of the I passes through the pipe 26 conveyor so that a substantially constant weight discharge can be expected. The weighing conveyor is equipped with a sensing device which transmits a weight information signal as indicated at 11 to the chemical proportiorn ing control. This control unit is arranged to transmit operating impulses as indicated at 12 to the gate 10 which regulates the flow of material to the Weighing conveyor.

The chemical proportioning control is an instrument obtainable in the open market designed to receive signals from various components of a system and to transmit operating impulses whose effect corresponds to the signals received. In the present system it not only controls the rate of supply of the raw paper making fiber but, as presently will appear,- the other two components, viz. the caustic digestant liquor and the fresh water.

The digestant or white liquor is delivered to the mixing conveyor at a rate commensurate to the rate of delivery to this conveyor of the raw fiber. The supply of white liquor comes from caustic tank No. 1 or caustic tank No. 2, having connections from caustic storage through a flow meter 12 connected to a recording and totalizing meter. Valves are provided between the two tanks so that the liquor can be drawn from one while the other is being filled from storage. The delivery pipe 13 leads to a caustic heater through a pump 14. .The heater is supplied with steam through a pipe line 15 and a series of valves which are regulated by a temperature control thermostat 15. This, in turn, is regulated by a temperature controlling device 16 in the discharge line running from the caustic heater through an automatically controlled valve 17, a recording flow meter 18, and a second valve 19 in the delivery line running to the mixing conveyor.

Similarly fresh water is supplied to the chemical fresh water heater through a supply line 20. The temperature of this heater is regulated by steam supplied through the line 21 and asystenrof valves whose operation is regu lated by a temperature control 22 governed by a thermostat 23. The fresh hot water then passes through a valve 24 and a recording flow meter 25 which. is arranged to transmit its flow information signals to the chemical pro portioning control from which the valve 24 is automatically adjusted to correspond to the indications. thus received. After leaving the flow meter 25 the hot water in controlled amount and delivers to the white liquor pipe line at a point just beyond the flow meter 18. The mixed white liquor and fresh hot water then passes through the valve 19 which, as already explained, is regulated by impulses from the chemical proportioning control and is delivered to the mixing conveyor. If desired the pipe 26 may lead directly to the mixing conveyor instead of to the white liquor line as shown. From the foregoing description it will be apparent that up to this point the system automatically insures delivery to the mixing conveyor (1) the raw fiber, (2) the white liquor, and (3) water in exactly the proper proportion as determined by the chemical proportioning control in response to the actual instantaneous supply of each component; that is to say, if the rate of delivery of the raw fiber increases for any reason, the rate of delivery of the moisture comprising white liquor and hot water is automatically increased exactly to balance it. The manner in which the indications of the flow meters and weighing conveyor are transmitted to the chemical proportioning control and the governing impulses are transmitted from it to the various valves is of secondary importance. As actually installed these weight and flow indications and governing impulses are transmitted by compressed air but electrical means may be employed with equally satisfactory results.

The regulated volume of a controlled density of digestant liquor is fed in, preferably as a spray, at the inner end of the mixing conveyor and in the immediate vicinity of the area wherein the raw fiber enters the mixing conveyor. One satisfactory type of mixing conveyor comprises an open U-shaped trough in which rotates a screw conveyor having blending characteristics. The entire length of the trough may be approximately 15 ft. and impregnation of the fiber will be nearly completed in the first ft. of travel imparted to it by the screw.

The completely impregnated fibre is discharged from the mixing conveyor by gravity into a combined hopper and feeder wherein the digestant liquor is expressed from the fiber and passed through a discharge pipe 27 and funnel 28 to an open type screen 29 where it is clarified and then pumped under pressure by a pump 30 to the digester or wasted to the sewer. Meanwhile the compressed fiber is delivered through a conduit 31 to the digester. This particular phase of the impregnation and circulation of the digestant liquor is disclosed in one satisfactory form in United States Patent No. 2,771,361, November 20, 1956, Birdseye. I

The digester is heated by steam admitted through the valve 32 and temperature within the digester is recorded by the temp. recorder connected thereto. The digesting phase of the process is carried out in the digester under conditions of heat and atmospheric pressure and finally the digester fibre is expelled from the digester through a duct 33 to a blow tank or other receptacle.

When the process is applied to the production of paper pulp from bagasse it will be seen that the system above described is particularly designed for (l) weighing the bagasse, (2) controlling the flow of bagasse, and (3) adding controlled amounts of white liquor and water to the product in proportion to the flow rate of bagasse. The weighing conveyor produces a pneumatic signal cor responding to the weight of the wet bagasse passing maximum dry fiber weight of lSO'tons per 24 hours is desired, the controller would be calling for 167 tons of total wet weight.

While the treatment of bagasse has been particularly described, it should be understood that the invention may be usefully applied to the treatment of wood fiber and this is included in the term raw vegetable fiber as herein used.

Having thus disclosed my invention and described an illustrative manner of carrying out my improved process, I claim as new and desire to secure by Letters Patent:

1. The process of converting raw bagasse stock into paper pulp which includes the steps of continuously delivering to a digester in separate paths and as components for making paper pulp (l) raw bagasse stock, (2) white liquor, and (3) Water, mechanically and continuously recording at a central station the rate of delivery of each of said components by sending weight and flow information signals thereto from points in the separate paths of said components, and automatically controlling from said central station the rate of feed of each component by sending therefrom control impulses operative in their effect in accordance with the information signals received.

2. The process of converting raw vegetable stock into paper pulp which includes the steps of passing the raw stock continuously through a Weighing station and methrough it and this signal is mechanically indicated in the chemical proportioning control and responded to in the manner already explained. The overall system is designed for either manual or automatic operation and is so designed that the transfer from manual to automatic, or from automatic to manual control may be easily carried out. The'total wet weight capacity of the weighing conveyor is 300 metric tons per 24 hours. The total dry weight of the system is 150 tons per 24 hours. For example, if the moisture content of the incoming bagasse is 50% and a maximum dry fiber weight of 150 tons per 24 hours is desired, the controller would be calling for 300 tons for 24 hours of the total wet weight. If on the other hand the moisture content is only 10% and a chanically recording the rate of its travel thereat in weight per unit of time by weight information signals transmitted to a remote control station, flowing digestant liquor in a separate path to the raw stock and recording its rate of flow at the same control station by flow information signals, and then automatically governing both the rate of travel of the raw stock and of the digestant liquor in response to the said weight and flow information signals -eceived by control impulse transmitted from the control station corresponding to the information signals.

3. Apparatus of the class described comprising means for continuously and separately delivering to a digester as components for making paper pulp (l) raw fibrous material, (2) white liquor, and (3) hot water, compressed air connections for transmitting to a central station weight and flow information signals proportional to the instantaneous rate of delivery of each of said components, and compressed air connections controlled from said central station to vary the rate of feed for each com ponent by continuous control impulses corresponding to the weight and flow information signals received and generated at said central station.

4. The process 'of converting raw vegetable stock into paper pulp which includes the steps of advancing the raw stock continuously to a digester at a uniform rate of weight compensated for variations in its moisture content, separately supplying and continuously adding hot water to the stock in an amount proportional to the weight advanced, and separately supplying and continuously adding white liquor to the aqueous mixture thus formed in an amount proportional to the actual instantaneous supply of the said components, continuously recording by compressed air information signals at a central station the rate of supply of each of said components,

and continuously controlling the rate of supply of hot water and white liquor by compressed air control impulses dispatched from said central station and operating in the supply lines of the respective liquid components.

5. The process of converting raw bagasse stock into paper pulp in which the raw stock is continuously advanced to amixing conveyor and there mixed with a separately supplied solution of water and caustic, characterized by the steps of mechanically forming a series of weight information signals varying in accordance wi h the rate of raw stock feed and transmitting the weight signals to a central station, mechanically forming anoth r series of flow information signals varying in accordance g with the rate of water and caustic flow and transmitting 1,710,375 Mourlaque Apr. 23, 1929 them to said station, and automatically controlling the 1,876,396 Butterfield Sept. 6, 1932 rate of raw stock feed and the rate of water and caustic 1,876,522 Vazuez Sept. 6, 1932 flow by control impulses dispatched from said central 1,922,366 Heritage et al Aug. 15, 1933 station and whose efi'ect corresponds to the information 5 2,409,524 Ahlfors Oct. 15, 1946 signals formed as above stated. 2,771,361 Birdseye et a1. Nov. 20, 1956 References Cited in the file of this patent QTHER REFIERENCES UNITED STATES PATENTS Perry. Chemical Engineers Handbook, 3rd Edition,

10 McGraw-Hill, 1950, pages 1293, 1265-1268, 1291-4295 1,155,741 Lee Oct. 5, 1915 andl309-1337. 

2. THE PROCESS OF CONVERTING RAW VEGETABLE STOCK INTO PAPER PULP WHICH INCLUDES THE STEPS OF PASSING THE RAW STOCK CONTINUOUSLY THROUGH A WEIGHING STATION AND MECHANICALLY RECORDING THE RATE OF ITS TRAVEL THREAT IN WEIGHT PER UNIT OF TIME BY WEIGHT INFORMATION SIGNALS TRANSMITTED TO A REMOTE CONTROL STATION, FLOWING DIGESTANT LIQUOR IN A SEPARATE PATH TO THE RAW STOCK AND RECORDING ITS RATE OF FLOW AT THE SAME CONTROL STATION BY FLOW INFORMATION SIGNALS, AND THEN AUTOMATICALLY GOVERNING BOTH THE RATE OF TRAVEL OF THE RAW STOCK AND OF THE DIGESTANT LIQUOR IN RESPONSE TO THE SAID WEIGHT AND FLOW INFORMATION SIGNALS RECEIVED BY CONTROL IMPULSE TRANSMITTED FROM THE CONTROL STATION CORRESPONDING TO THE INFORMATION SIGNALS. 